NPC output dropping from 24 to 16 bits while recording


#1

I am using the NPC to output via USB to my MacBook Pro running Mavericks and using vinyl studio to store the files. I have the NPC set to output PCM at 24/96. I’ve tried recording to both AIFF and FLAC. Also, I have the I2S output on the NPC going to my DirectStream for listening while ripping. I make sure the settings in vinyl studio are set to PCM 24/96. When I start recording, everything looks ok initially (NPC is outputting at 24/96). However, after a song or two, I can see the bits on the display of the DirectStream drop from 24 to 16. Also when I play back the file that was recorded into the DirectStream, it starts as 24/96 for a half second the drops down to 16/96. This does not change whether I use flac or aiff.

This is would appear to be some kind of hardware issue in the NPC but I’m not sure. I have the latest firmware in both the NPC and the DirectStream.

Any help would be greatly appreciated.

Thanks


#2

One more thing to add. The bits on the DirectStream does not constantly stay at 16 after the initial drop while playing. Sometimes it jumps back to 24 for a second and then back to 16. It may do this a few times in a row, then not do it for 5 minutes straight. It’s pretty inconsistent.


#3

Wow, this is a first. Not sure what the heck that’s about. The first thing I would do is disconnect from the computer altogether and stream just to the DirectStream and see if the same thing happens. I suspect it will not. If that’s the case, then there’s something flaky going on with the computer and program that’s switching the NPC back and forth. Let us know what you find.


#4

This is indeed incredibly odd. I share Paul’s suspicion that the compute is doing something odd.

I like the idea of trying disconnecting the computer and watching what happens with only the DS receiving the signal. My guess it will work fine with nothing untoward happening.

It would also be interesting to see what happens with the output going only to the computer. Additionally, do you have the capability to send something other than USB to the computer? USB is bi-directional; S/PDIF, not. I bet nothing odd happens if the compute is receiving optical or coax S/PDIF.


#5

Thanks for the responses guys. Both of your suspicions are correct. When disconnecting the USB and streaming directly from the NPC to the DirectStream via I2S, the output remains at a steady 24/96 as indicated by the LCD of the DirectStream.

What I did next was plug in the USB right after this, and the input on the DirectStream remained at 24/96. However, in spite of telling vinyl studio to record at 24/96, the display on the DirectStream switched to 16/96 when I began recording with vinyl studio.

I do not currently have a way to send PCM to my MacBook other than USB. It has a built in optical port which I use with my DL III in my headphone system, but I don’t believe it works as an input.

My my next step will be to use a different application such as audacity to see if the same thing happens. If not, then I think we’ve narrowed it down. I’ll report back with my findings.

Thanks,

John


#6

Nice progress and this makes it unlikely to be a hardware problem.

In addition to double checking all settings in Vinyl Studio and the Mac itself - audio/midi to 96/24 for example - I suggest trying another format such as 44/24 to see if the bit-depth will hold.

Just for diagnostic purposes I would remove the connection to the DS when recording to the Mac.

Hopefully, one of our Mac types will be along soon to help.


#7

If your MBP has a mic input jack it should accept an optical input. I’ve used the one on my 2010 MBP to record the digital track off of laser discs.


#8

I would contact Paul Sanders of Vinyl Studio. He actually answers email and is very responsive. Vinyl Studio is a great program and Paul will get it sorted out for you.


#9

Here are some updates on my findings.

I decided to do a test using Audacity instead of VinylStudio. I recorded a few sample files, setting Audacity to 24/96. Some samples I recorded with the I2S connection streaming to the DirectStream, and some with the I2S completely disconnected. When playing back all samples into the DirectStream from the MacBook Pro, the output stayed at 24/96 (as shown on the LCD of the DirectSream).

As for using the optical port on the MacBook, this would be a good diagnostic, but ultimately I will not be using optical for archiving vinyl, as I would think the USB transfer provides better fidelity, and the ability to send DSD when desired.

At this point it would seem as though the issue lies with VinylStudio, or with something in my Mac. I’ve heard you can do a “USB Reset” on MacBooks, and that this sometimes resolves audio-related issues with USB. Has anyone ever done this and had any success?

Paul, I will contact Paul Sanders of VinylStudio to get his input on this.

Thanks,

John


#10

Good progress.

Please keep us updated. I am interested in learning what Paul Sanders suggests.


#11

This is the response I received from Paul Sanders:

"Hi,

There is in fact an issue with the NPC firmware that causes it to deliver 16 bit data (in a 24 bit envelope) under some circumstances when recording via USB. I think you must be tripping over that. PS Audio are working on a fix but are not yet ready to release it. I suggest you mention this to them and enquire when the updated firmware will be available."

Is this true? Hopefully someone from PS Audio can answer this question.

Thanks,

John


#12

Ahh, the problem we’re currently working on concerns 176kHz only. For some reason there’s a bug that when using this frequency, the sample rate changes in USB. It didn’t sound like that was the issue, otherwise I would have brought it up.


#13

Ah ok I see. I’ve contacted Paul Sanders again regarding this. Not sure where to go with this now. Might be time to consider using an alternative application for archiving vinyl, although I really do like the feature set in VinylStudio, especially given its price.


#14

This is my last correspondence with Paul Sanders:

"Hi,

No, VinylStudio has been checked, the issue is definitely in the NPC firmware. I have asked PS Audio to help you get the fix."

I’ve asked him to give me the name of who he’s in contact with, but it would probably be best if we all got on the same page here, since there seems to be a misunderstanding on one side here. It would also be much more efficient than me playing middle man for these communications.

John


#15

Yup it’s us, I am on it.


#16

You may have tried this but Macs are notoriously flakey for this changing feature.

What I do before launching my recording software is open the “Audio MIDI Setup” preference and ensure it is set to 24/96.
If it was something else, I see the NPC auto-adjust, and in fact I occasionally toggle it to make sure they are talking.

I also open the Preferences -> Sound and ensure that here too the settings are as expected.

Then I launch my capture software (I prefer Sound Studio or Amadeus Pro to VinylStudio personally).
I never seem to have it change during capture at this point, but often when I come back to the Mac hours or days later I find it has reverted in the Audio MIDI-setup screen. I have talked with many vinyl rippers who see this behavior and have going back 4 or 5 years at least. I usually just leave the MIDI screen open anymore.

Now, all that said, I did have a problem about a month ago where a lot of my 24/96 rips came out showing they were full 24/96, but when I converted to FLAC they compressed like mad, over 60% which is crazy small, like a folded mono or something. Normally I get about 30-35% compression converting to FLAC (from AIFF which I capture in). The problem mysteriously went away and I never did really figure out what happened, my audio players, MediaInfoMac, and other tools still confirm the files are all 24/96, but I know something weird was afoot.

But the Audio MIDI-setup is a common issue you should at least try out if you have not solved it yet.